US President Donald Trump said on Monday that the Tuesday deadline he has set for Iran to make a deal is final, adding that Iran's proposal was significant but not good enough.

"They made a proposal, and it's a significant proposal. It's a significant step. It's not good enough," Trump said of Iran.

"It could end very quickly, the war, if they do what they have to do. They have to do certain things. They know that, they've been negotiating I think in good faith," he said while at an annual White House Easter event.